It is desirable to reduce the size of an implantable cardioverter/defibrillator (ICD) in order to improve patient comfort, reduce risk of erosion through the skin, and facilitate pectoral placement. Because the batteries and capacitors account for a large portion of the defibrillator, reducing the defibrillation threshold (DFT), or the amount of energy required to defibrillate the heart, is key to allowing the device size to be reduced. Internal defibrillation energies are typically between 5 and 40 J, depending on the individual patient and his condition, the lead system, and the defibrillation waveform. Using less energy to defibrillate has the added benefit of improving patient comfort and reducing trauma to the patient's cardiac conduction system.
Many techniques have been used in the past to reduce DFTs. These include the use of modified electrodes, described by Ideker et al. in "Current Concepts for Selecting the Location, Size and Shape of Defibrillation Electrodes," PACE 1991, 14:227-240, and described by Lang et at. in "Implantable Cardioverter Defibrillator Lead Technology: Improved Performance and Lower Defibrillation Thresholds," PACE 1995, 18:548-559.